Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1979 The interaction and reactivity of nitric oxide and carbon monoxide on ruthenium surfaces Edward Edwards Quick Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Physical Chemistry Commons Recommended Citation Quick, Edward Edwards, "The interaction and reactivity of nitric oxide and carbon monoxide on ruthenium surfaces " (1979). Retrospective Theses and Dissertations. 7305. https://lib.dr.iastate.edu/rtd/7305 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 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ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WC1R 4ËJ, ENGLAND 8010256 QUICK, EDWARD EDWARDS THE INTERACTION AND REACTIVITY OF NITRIC-OXIDE AND CARBON- MONOXIDE ON RUTHENIUM SURFACES Iowa State University PH.D. 1979 University Microfilms 1 ntGrnâtiOnâl 300 N. Zeeb Road, Ann Arbor. MI 48106 18 Bedford Row, London WC1R4EJ, England PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark . 1. Glossy photographs 2. Colored illustrations 3. Photographs with dark background '4. Illustrations are poor copy 5. orint shows through as there is text on both sides of page 6. Indistinct, broken or small print on several pages throughout 7. Tightly bound copy with print lost in spine 8r Computer printout pages with indistinct print 9. Page(s) lacking when material received, and not available from school or author 10. 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Iowa 1979 11 TABLE OP CONTENTS Page INTRODUCTION 1 LITERATURE SURVEY 4 Reaction Kinetics 4 Reactant Surface Interactions 17 EXPERIMENTAL 30 Reactor System Design 31 Ruthenium Crystal Preparation 37 Kinetic Procedure 4l Thermal Desorption Techniques 45 LEED/Auger Procedure 47 X-Ray Photoelectron Spectroscopy Experiments 50 Materials 50 RESULTS AND DISCUSSION 52 Kinetics Introduction 52 Surface Characterization 62 LEED/Auger characterization. 62 XPS characterization 101 Thermal desorption spectroscopy 113 Exchange Studies 124 Rate Reproducibility and Mechanistic Considerations 131 Ill SUMMARY AND SUGGESTIONS FOR FUTURE INVESTIGATIONS 18? LITERATURE CITED I90 ACKNOWLEDGMENT I98 APPENDIX 200 1 INTRODUCTION During the past ten years an extensive effort has been made in the field of catalytic chemistry to describe the nitric oxide reduction system. This interest was precipi­ tated by the 1970 Clean Air Act calling for the diminution of nitric oxide emission from automobile exhaust. Since then literally thousands of conceivable catalysts have been tested but it is safe to say that transition metal oxides and noble metal catalysts have shown the most promise. A difficulty arising in these studies is that no given catalytic material will promote the reduction at the required rate and lead to a specified product distribution. The problem is multiplied by the fact that the exhaust composition usually consists of not just nitric oxide and carbon monoxide but also hydro­ carbons, oxygen, water and hydrogen (1) as well as a number of inert components. This leads to up to eleven different thermodynamically possible reactions occurring in a given catalyst bed. The hydrogen-CO oxidation catalysts that were rapidly developed during the early 1970's can be attributed solely to the wealth of fundamental studies conducted over previous years in defining the mechanisms of the possible reactions and the characterization of the catalysts investigated. Major research thrusts in this area led to a decreased priority in the area of NO research and thus contributed to 2 the less advanced development of NO^ reduction catalysts at the present time. Without the necessary kinetic and mechan­ istic information available, suitable catalysts that would reduce NO^ emissions to meet Federal standards have not resulted. This has, therefore, brought forth a new signifi­ cance to the pursuance of fundamental studies between the active components comprising motor vehicle exhausts. Since it is difficult to obtain meaningful kinetic data that can be related to a specific mechanism from a system where many reactions are possible, only one reductant was chosen for investigation, namely carbon monoxide. The reaction between nitric oxide and carbon monoxide can lead to two possible nitrogen-containing products: nitrous oxide and molecular nitrogen as depicted in the following reactions: 2N0 + CO COp + NgO (1) 2N0 + 2C0 ^2^ 2CO2 + Ng (2) Of the catalysts that have been investigated, metallic ruthenium is of considerable interest. It is favored not only for its high activity but also because under exhaust conditions it has been shown to be more selective to the formation of Ng over ammonia (2-8) than platinum or rhodium. Due to these reasons as well as to the interesting surface chemistry involving ruthenium, a study has been undertaken utilizing a single crystal ruthenium disc of the 3 (102) orientation. This thesis will describe a multi-faceted investigation incorporating not only kinetic and isotopic studies, but also employing the low energy electron diffraction (LEED), Auger electron spectroscopy CAES), x-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS) techniques. Prom the spectroscopies utilized, the surface characteristics of the ruthenium catalyst have been probed both before and following inter­ action with the reactants so as to discern the nature of the adsorbed intermediates as a function of temperature and pressure. By incorporating kinetic and isotopic studies into this investigation, a mechanism consistent with the surface characterization data will be developed. Previous kinetic work has led to only a qualitative understanding of the nitric oxide reduction system. The conditions under which this work has been performed —9 are from 10 to 10 Torr reactant partial pressures with substrate temperatures ranging from room temperature to 1000°C. The kinetic reaction conditions are of a more limited nature as the partial pressures studied were in the 10~^ to 10 Torr range using a catalyst temperature of 475°C. This dissertation will be divided into three sections comprising a survey of literature relevant to the nitric oxide reduction reactions on ruthenium, an experimental procedures section and finally a presentation and discussion of the results. 4 LITERATURE SURVEY This survey will be divided into two main areas. The first area will consist of a literature